Fix bootstrap exception

Author: liufengyun

compiler/src/dotty/tools/dotc/transform/SpecializeFunctions.scala

@@ -18,23 +18,23 @@ class SpecializeFunctions extends MiniPhase with InfoTransformer {
 
   /** Transforms the type to include decls for specialized applys  */
   override def transformInfo(tp: Type, sym: Symbol)(using Context) = tp match {
-    case tp: ClassInfo if !sym.is(Flags.Package) && derivesFromFn012(sym) =>
+    case tp: ClassInfo if !sym.is(Flags.Package) =>
       val newApplys = new mutable.ListBuffer[Symbol]
 
       var arity = 0
       while (arity < 3) {
         val func = defn.FunctionClass(arity)
         if (tp.derivesFrom(func)) {
-          val paramTypes = tp.cls.typeRef.baseType(func).argInfos
-          val isSpecializable =
+          lazy val paramTypes = tp.cls.typeRef.baseType(func).argInfos
+          def isSpecializable =
             defn.isSpecializableFunction(
               sym.asClass,
               paramTypes.init,
               paramTypes.last
             )
 
           val apply = tp.decls.lookup(nme.apply)
-          if (isSpecializable && apply.exists) {
+          if (apply.exists && isSpecializable) {
             val specializedMethodName = specializedName(nme.apply, paramTypes)
             val applySpecialized = newSymbol(
               sym,
@@ -70,7 +70,11 @@ class SpecializeFunctions extends MiniPhase with InfoTransformer {
 
     val applyBuf = new mutable.ListBuffer[Tree]
     val newBody = tree.body.mapConserve {
-      case ddef: DefDef if ddef.name == nme.apply && ddef.vparamss.length == 1 =>
+      case ddef: DefDef
+        if ddef.name == nme.apply &&
+          ddef.vparamss.length == 1 &&
+          ddef.vparamss.head.length < 3
+      =>
         val paramTypes = ddef.vparamss.head.map(_.symbol.info)
         val retType = ddef.tpe.widen.finalResultType
 
@@ -94,7 +98,8 @@ class SpecializeFunctions extends MiniPhase with InfoTransformer {
       case x => x
     }
 
-    cpy.Template(tree)(body = applyBuf.toList ::: newBody)
+    if applyBuf.isEmpty then tree
+    else cpy.Template(tree)(body = applyBuf.toList ::: newBody)
   }
 
   /** Dispatch to specialized `apply`s in user code when available */